INDIANAPOLIS, Indiana -- An Indiana couple says the little girl, Natalia, they adopted from Ukraine is actually an adult with dwarfism and tried to hurt and kill them on multiple occasions, Michael Barnett said in an interview with Good Morning America.

"We were told by doctors, 'This person is a sociopath. This person is a con artist. You are all in danger,'" Michael Barnett said.

Michael and his now ex-wife Kristine Barnett thought they were adopting an adorable 6-year-old girl from Ukraine back in 2010.

The couple is accused of neglecting their adopted daughter Natalia after court documents claim they rented an apartment for the girl in 2013 and left her there alone, while they moved out of the country with the rest of the family.

The Barnetts tell GMA, Natalia is not who she says she is. They claim she's an adult and that she was attempting to cause them harm.

"Natalia would do things like place clear thumbtacks on the stairs face up so that when we would walk up the stairs we would be stepping on thumbtacks to pain and injure ourselves," Michael Barnett said.

Michael said his wife discovered evidence of a monthly menstrual cycle and that Natalia, when confronted, said she did have one and had been hiding it from them.

Shortly after Natalia attempted to poison Kristine by pouring a bottle of Pine Sol into her coffee mug, Michael said.

"She had attempted to kill my wife for the second time, this time by trying to pull her into an electric fence," Michael said.

The couple tried to press charges against her, but instead she was pushed into a hospital system.

Natalia suffers from a rare form of dwarfism and Michael said they quickly noticed some suspicious behavior, including developmental changes consistent with adults.

He claimed that doctors, testing and even a court ruling led them to believe she was actually born in 1989.

"In 2012, based on evidence presented to the court, the Marion County Superior Court ruled that her birth year would be changed from 2003 to 1989, effectively changing her from eight to 22 years old," Michael said.

It's still unclear exactly how old the girl is. Based on the Ukrainian birth certificate that the Barnetts were originally given at adoption, she would be about 16 years old. But if the court system's decision to change her birth year was accurate, she would be around 30.

Officials believe Natalia was a minor when the Barnetts moved to Canada, and they are both facing charges of neglect including endangering a dependent's life and abandoning or cruelly confining a dependent.

Michael's lawyers have filed a motion to dismiss the case based on inaccurate information.